Purpose
We have previously reported on our technique to deliver intensity-modulated radiotherapy (IMRT) to the entire pleura while attempting to spare the lung in patients with malignant pleural mesothelioma (MPM). Herein, we report a detailed pattern-of-failure analysis in patients with MPM who were unresectable or underwent pleurectomy/decortications (P/D), uniformly treated with hemithoracic pleural IMRT.
Methods
Sixty-seven patients with MPM were treated with definitive or adjuvant hemithoracic pleural IMRT between 11/2004 and 5/2013. Pretreatment imaging, treatment plans, and post-treatment imaging were retrospectively reviewed to determine failure location(s). Failures were categorized as in-field (within the 90% isodose line), marginal (<90% and ≥50% isodose lines), out-of-field (outside the 50% isodose line), or distant.
Results
The median follow-up was 24 months from diagnosis and the median time to in-field local failure from the end of radiotherapy was 10 months. Forty-three in-field local failures (64%) were found with a 1- and 2-year actuarial failure rate of 56% and 74%, respectively. For patients who underwent P/D versus those who received a partial pleurectomy or were deemed unresectable, the median time to in-field local failure was 14 months versus 6 months, with 1- and 2-year actuarial in-field local failure rates of 43% and 60% versus 66% and 83%, respectively (p=0.03). There were 13 marginal failures (19%). Five of the marginal failures (38%) were located within the costomediastinal recess. Marginal failures decreased with increasing institutional experience (P = .04). Twenty-five patients (37%) had out-of-field failures. Distant failures occurred in 32 patients (48%).
Conclusion
After hemithoracic pleural IMRT, local failure remains the dominant form of failure pattern. Patients treated with adjuvant hemithoracic pleural IMRT after P/D experience a significantly longer time to local and distant failure than patients treated with definitive pleural IMRT. Increasing experience and improvement in target delineation minimize the incidence of avoidable marginal failures.